A laccolith is a sheet intrusion (or concordant pluton) that has been injected between two layers of sedimentary rock. The pressure of the magma is high enough that the overlying strata are forced upward, giving the laccolith a dome or mushroom-like form with a generally planar base.

A laccolith intruding into and deforming strata

Laccolith exposed by erosion of overlying strata in Montana

Pink monzonite intrudes within the grey Cambrian and Ordovician strata near Notch Peak, Utah

Laccoliths tend to form at relatively shallow depths and are typically formed by relatively viscous magmas, such as those that crystallize to diorite, granodiorite, and granite. Cooling underground takes place slowly, giving time for larger crystals to form in the cooling magma. The surface rock above laccoliths often erodes away completely, leaving the core mound of igneous rock. The term was first applied as laccolite by Grove Karl Gilbert after his study of intrusions of diorite in the Henry Mountains of Utah in about 1875.

It is often difficult to reconstruct shapes of intrusions. For instance, Devils Tower in Wyoming was thought to be a volcanic neck, but study has revealed it to be an eroded laccolith.^[1] The rock would have had to cool very slowly so as to form the slender pencil-shaped columns of phonolite porphyry seen today. However, erosion has stripped away the overlying and surrounding rock, and so it is impossible to reconstruct the original shape of the igneous intrusion; that rock may not be the remnant of a laccolith. At other localities, such as in the Henry Mountains and other isolated mountain ranges of the Colorado Plateau, some intrusions demonstrably have shapes of laccoliths. The small Barber Hill syenite-stock laccolith in Charlotte, Vermont, has several volcanic trachyte dikes associated with it. Molybdenite is also visible in outcrops on this exposed laccolith. In Big Bend Ranch State Park, at the southwesternmost visible extent of the Ouachita orogeny, lies the Solitario.^[2] It consists of the eroded remains of a laccolith, presumably named for the sense of solitude that observers within the structure might have, due to the partial illusion of endless expanse in all directions.^[2]

One of the largest laccoliths in the United States is Pine Valley Mountain in the Pine Valley Mountain Wilderness area near St. George, Utah

There are many examples of possible laccoliths on the surface of the Moon.^[3] These igneous features may be confused with impact cratering.

See also[link]

• Batholith
• Dike
• Hydrolaccolith
• Lopolith
• Sill
• Stock

References[link]

• Blatt, Harvey and Robert J. Tracy, 1996, Petrology: Igneous, Sedimentary and Metamorphic, 2nd ed., pp. 13-15, Freeman, ISBN 0-7167-2438-3</ref>
• Jules D. Friedman and Curtis Huffman, Jr., coordinators, "Laccolith Complexes of Southeastern Utah: Time of Emplacement and Tectonic Setting -- Workshop Proceedings", United States Geological Survey Bulletin 2158, 1998.

Devils Tower National Monument
IUCN category V (protected landscape/seascape)
Devils Tower, 2005
Location	Crook County, Wyoming, USA
Nearest city	Hulett, Wyoming
Coordinates	44°35′25″N 104°42′55″W / 44.59028°N 104.71528°W / 44.59028; -104.71528Coordinates: 44°35′25″N 104°42′55″W / 44.59028°N 104.71528°W / 44.59028; -104.71528
Area	1,346 acres (545 ha)[1]
Established	September 24, 1906 (1906-September-24)
Visitors	395,203 (in 2011)[2]
Governing body	National Park Service

Devils Tower (Lakota: Matȟó Thípila or Ptehé Ǧí, which means “Bear Lodge” and ”brown buffalo horn”, respectively) (Arapaho: Wox Niiinon ^[3]) is an igneous intrusion or laccolith located in the Black Hills near Hulett and Sundance in Crook County, northeastern Wyoming, above the Belle Fourche River. It rises dramatically 1,267 feet (386 m) above the surrounding terrain and the summit is 5,112 feet (1,558 m) above sea level.

Devils Tower was the first declared United States National Monument, established on September 24, 1906, by President Theodore Roosevelt. The Monument's boundary encloses an area of 1,347 acres (545 ha).

In recent years, about 1% of the Monument's 400,000 annual visitors climb Devils Tower, mostly through traditional climbing techniques.^[4]

Name[link]

Devils Tower, 1900

Tribes including the Arapaho, Crow, Cheyenne, Kiowa, Lakota, and Shoshone had cultural and geographical ties to the monolith before European and early American immigrants reached Wyoming. Their names for the monolith include: Aloft on a Rock (Kiowa), Bear's House (Cheyenne, Crow), Bear's Lair (Cheyenne, Crow), Bear's Lodge (Cheyenne, Lakota), Bear's Lodge Butte (Lakota), Bear's Tipi (Arapaho, Cheyenne), Tree Rock (Kiowa), and Grizzly Bear Lodge (Lakota).

The name Devil's Tower originated in 1875 during an expedition led by Col. Richard Irving Dodge when his interpreter misinterpreted the name to mean Bad God's Tower. This was later shortened to the Devil's Tower.^[5] All information signs in that area use the name "Devils Tower", following a geographic naming standard whereby the apostrophe is eliminated.^[6]

In 2005, a proposal to recognize several American Indian ties through the additional designation of the monolith as Bear Lodge National Historic Landmark met with opposition from the US Representative Barbara Cubin, arguing that a "name change will harm the tourist trade and bring economic hardship to area communities".^[7]

Geological history[link]

Devils Tower in geological context. The oval-shaped mesa around the Tower suggests the old volcano's shape. The red rock is the Permian-Triassic Spearfish Formation, and above that is the younger, white Gypsum Springs Formation. Aerial photo, 2010.

Red sandstone and siltstone cliffs above the Belle Fourche River

Map of Wyoming National Parks and landmarks, showing Devils Tower (upper right) far east of Yellowstone (upper left), north across the state from Cheyenne.

The landscape surrounding Devils Tower is composed mostly of sedimentary rocks. The oldest rocks visible in Devils Tower National Monument were laid down in a shallow sea during the Triassic period, 225 to 195 million years ago. This dark red sandstone and maroon siltstone, interbedded with shale, can be seen along the Belle Fourche River. Oxidation of iron minerals causes the redness of the rocks. This rock layer is known as the Spearfish Formation.

Above the Spearfish formation is a thin band of white gypsum, called the Gypsum Springs Formation. This layer of gypsum was deposited during the Jurassic period, 195 to 136 million years ago.

Created as sea levels and climates repeatedly changed, gray-green shales (deposited in low-oxygen environments such as marshes) were interbedded with fine-grained sandstones, limestones, and sometimes thin beds of red mudstone. This composition, called the Stockade Beaver member, is part of the Sundance Formation. The Hulett Sandstone member, also part of the Sundance formation, is composed of yellow fine-grained sandstone. Resistant to weathering, it forms the nearly vertical cliffs which encircle the Tower itself.

About 65 million years ago, during the Paleogene Period, the Rocky Mountains and the Black Hills were uplifted. Magma rose through the crust, intruding into the existing sedimentary rock layers.

Theories of formation[link]

Geologists agree that Devils Tower was formed by the intrusion of igneous material, but they cannot agree on how, exactly, that process took place. Geologists Carpenter and Russell studied Devils Tower in the late 19th century and came to the conclusion that the Tower was formed by an igneous intrusion. Later geologists searched for further explanations. Several geologists believe the molten rock comprising the Tower might not have surfaced; other researchers are convinced the tower is all that remains of what once was a large explosive volcano.

In 1907, scientists Darton and O'Hara decided that Devils Tower must be an eroded remnant of a laccolith. A laccolith is a large mass of igneous rock which is intruded through sedimentary rock beds without reaching the surface, but makes a rounded bulge in the sedimentary layers above. This theory was quite popular in the early 20th century since numerous studies had earlier been done on laccoliths in the Southwest.

Other theories have suggested that Devils Tower is a volcanic plug or that it is the neck of an extinct volcano. Presumably, if Devils Tower was a volcanic plug, any volcanics created by it – volcanic ash, lava flows, volcanic debris – would have been eroded away long ago. Some pyroclastic material of the same age as Devils Tower has been identified elsewhere in Wyoming.

The igneous material that forms the Tower is a phonolite porphyry intruded about 40.5 million years ago,^[8] a light to dark-gray or greenish-gray igneous rock with conspicuous crystals of white feldspar.^[9] As the lava cooled, hexagonal (and sometimes 4-, 5-, and 7-sided) columns formed. As the rock continued to cool, the vertical columns shrank horizontally in volume and cracks began to occur at 120 degree angles, generally forming compact 6-sided columns. Superficially similar, but with typically 2 feet (0.61 m) diameter columns, Devils Postpile National Monument and Giant's Causeway are columnar basalt.

Devils Tower did not visibly protrude out of the landscape until the overlying sedimentary rocks eroded away. As the elements wore down the softer sandstones and shales, the more resistant igneous rock making up the tower survived the erosional forces. As a result, the gray columns of Devils Tower began to appear as an isolated mass above the landscape.

As rain and snow continue to erode the sedimentary rocks surrounding the Tower's base, more of Devils Tower will be exposed. Nonetheless, the exposed portions of the Tower still experience certain amounts of erosion. Cracks along the columns are subject to water and ice erosion. Erosion due to the expansion of ice along cracks and fractures within rock formations is common in colder climates – a prime example being the featured formations at Bryce Canyon National Park. Portions, or even entire columns, of rock at Devils Tower are continually breaking off and falling. Piles of broken columns, boulders, small rocks, and stones – or scree – lie at the base of the tower, indicating that it was once wider than it is today.

Native American folklore[link]

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A sign informs visitors of the American Indian heritage.

According to the Native American tribes of the Kiowa and Lakota Sioux, some girls went out to play and were spotted by several giant bears, who began to chase them. In an effort to escape the bears, the girls climbed atop a rock, fell to their knees, and prayed to the Great Spirit to save them. Hearing their prayers, the Great Spirit made the rock rise from the ground towards the heavens so that the bears could not reach the girls. The bears, in an effort to climb the rock, left deep claw marks in the sides, which had become too steep to climb. (Those are the marks which appear today on the sides of Devils Tower.) When the girls reached the sky, they were turned into the star constellation the Pleiades.

Another version tells that two Sioux boys wandered far from their village when Mato the bear, a huge creature that had claws the size of teepee poles, spotted them, and wanted to eat them for breakfast. He was almost upon them when the boys prayed to Wakan Tanka the Creator to help them. They rose up on a huge rock, while Mato tried to get up from every side, leaving huge scratch marks as he did. Finally, he sauntered off, disappointed and discouraged. The bear came to rest east of the Black Hills at what is now Bear Butte. Wanblee, the eagle, helped the boys off the rock and back to their village. A painting depicting this legend by artist Herbert A. Collins hangs over the fireplace in the visitor's center at Devils Tower.

In a Cheyenne version of the story, the giant bear pursues the girls and kills most of them. Two sisters escape back to their home with the bear still tracking them. They tell two boys that the bear can only be killed with an arrow shot through the underside of its foot. The boys have the sisters lead the bear to Devils Tower and trick it into thinking they have climbed the rock. The boys attempt to shoot the bear through the foot while it repeatedly attempts to climb up and slides back down leaving more claw marks each time. The bear was finally scared off when an arrow came very close to its left foot. This last arrow continued to go up and never came down.^[10]

Wooden Leg, a Northern Cheyenne, relates another legend told to him by an old man as they were traveling together past the Devils Tower around 1866-1868. An Indian man decided to sleep at the base of Bear Lodge next to a buffalo head. In the morning he found that both himself and the buffalo head had been transported to the top of the rock by the Great Medicine with no way down. He spent another day and night on the rock with no food or water. After he had prayed all day and then gone to sleep, he awoke to find that the Great Medicine had brought him back down to the ground, but left the buffalo head at the top near the edge. Wooden Leg maintains that the buffalo head was clearly visible through the old man's spyglass. At the time, the tower had never been climbed and a buffalo head at the top was otherwise inexplicable.^[11]

The buffalo head gives this story special significance for the Northern Cheyenne. All the Cheyenne maintained in their camps a sacred teepee to the Great Medicine containing the tribal sacred objects. In the case of the Northern Cheyenne, the sacred object was a buffalo head.^[12]

Recent history[link]

Ponderosa Pine forest east of Devils Tower

Fur trappers may have visited Devils Tower, but they left no written evidence of having done so. The first documented visitors were several members of Captain W. F. Raynold's 1859 Yellowstone Expedition. Sixteen years later, Colonel Richard I. Dodge escorted an Office of Indian Affairs scientific survey party to the massive rock formation and coined the name Devils Tower.^[13] Recognizing its unique characteristics, Congress designated the area a U.S. forest reserve in 1892 and in 1906 Devil's Tower became the nation's first National Monument.^[14]

The 1977 movie Close Encounters of the Third Kind used the formation as a plot element and as the location of its climactic scenes.^[15][16] Its release was the cause of a large increase in visitors to the monument.^[17]

Climbing[link]

The Devils Tower Trading Post in 2003

In recent years, climbing Devils Tower National Monument has increased in popularity. The first known ascent of Devils Tower by any method occurred on July 4, 1893, and is accredited to William Rogers and Willard Ripley, local ranchers in the area. They completed this first ascent after constructing a ladder of wooden pegs driven into cracks in the rock face. A few of these wooden pegs are still intact and are visible on the tower when hiking along the 1.3-mile (2.1 km) Tower Trail at Devils Tower National Monument. Over the following thirty years many climbs were made using this method before the ladder fell into disrepair. The man most famous for climbing the tower is Fritz Wiessner who summited with William P. House and Lawrence Coveney in 1937. This was the first ascent using modern climbing techniques. Wiessner led the entire climb free, placing only a single piece of fixed gear (piton) which he later regretted, deeming it unnecessary.

In 1941 George Hopkins parachuted on to Devils Tower, without permission, as a publicity stunt resulting from a bet. He had intended to descend by a rope dropped with him, but this failed to land on the tower summit. Hopkins was stranded for six days exposed to cold, rain and 50 mph winds before a mountain rescue team finally reached him and brought him down.^[18][19] His entrapment and subsequent rescue was widely covered by the media of the time.^[20]

Today hundreds of climbers scale the sheer rock walls of Devils Tower each summer. The most common route is the Durrance Route which was the second free route established in 1938. Today there are many established and documented climbing routes covering every side of the tower, ascending the various vertical cracks and columns of the rock. The difficulty of these routes range from relatively easy to some of the hardest in the world. All climbers are required to register with a park ranger before and after attempting a climb.

The Tower is sacred to several Native American Plains tribes, including the Lakota Sioux, Cheyenne and Kiowa. Because of this, many Indian leaders objected to climbers ascending the monument, considering this to be a desecration. The climbers argued that they had a right to climb the Tower, since it is on federal land. A compromise was eventually reached with a voluntary climbing ban during the month of June when the tribes are conducting ceremonies around the monument. Climbers are asked, but not required, to stay off the Tower in June. According to the PBS documentary In the Light of Reverence, approximately 85% of climbers honor the ban and voluntarily choose not to climb the Tower during the month of June. However, several climbers along with the Mountain States Legal Foundation sued the Park Service, claiming an inappropriate government entanglement with religion.^[21]

Gallery[link]

• 

  Devils Tower, 2003

• 

  Near the base of Devils Tower.

• 

  East face of Devils Tower.

• 

  Aerial photo of Devils Tower.

• 

  Close-up of the columns.

See also[link]

Four areas of Devils Tower National Monument on the National Register of Historic Places:

• Entrance Road (Devils Tower National Monument)
• Entrance Station (Devils Tower National Monument)
• Old Headquarters Area Historic District
• Tower Ladder (Devils Tower National Monument)

References[link]

Bibliography[link]

• Marquis, Thomas B. (2003). Wooden Leg: A Warrior Who Fought Custer. Lincoln, Neb.: University of Nebraska Press, Bison Books. ISBN 0-8032-8288-5. OCLC 52423964, OCLC 57065339. Wooden Leg: A Warrior Who Fought Custer at Google Books.

External links[link]

Wikimedia Commons has media related to: Devils Tower National Monument

• Devils Tower National Monument. National Park Service.
• The short film Tower of Stone is available for free download at the Internet Archive [more]